Ultrasonic surgical apparatus with power reduction

ABSTRACT

An ultrasonic surgical includes a probe with an operative edge or surface at a distal end, an electromechanical transducer connected to the probe, and an activation circuit connected to the transducer for supplying thereto an electrical waveform having an ultrasonic frequency and an amplitude. The activation circuit includes a signal generator and further includes a power reduction circuit operatively connected to the signal generator for inducing the signal generator to automatically reduce the amplitude of the waveform upon a sensing by the power reduction circuit of reduced load on the probe.

BACKGROUND OF THE INVENTION

This invention relates to an ultrasonic surgical apparatus. Moreparticularly, this invention relates to an ultrasonic bone cuttingapparatus. The invention also relates to an associated surgical method.

Ultrasonic surgical blades for cutting bone have known for severalyears. U.S. Pat. No. 6,379,371 and U.S. Pat. No. 6,443,969 disclose sucha surgical blade. Ultrasonic bone cutting tools exhibit significantadvantages over more traditional instruments such as power saws androtary cutters. Ultrasonic bone cutting blades have been devised forenabling a separation of bone and soft tissue, along an interfacebetween the two, with a minimum of damage to the soft tissue. Such aninstrument is disclosed in U.S. Pat. No. 8,343,178.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide and improvedultrasonic bone cutting apparatus.

A more particular object of the present invention is to provide anultrasonic bone cutting apparatus the use of which entails a reducedprobability of damage to soft tissues adjacent to a bone being cut.

Another particular object of the present invention is to provide anultrasonic bone cutting apparatus configured to automatically protectsoft tissues adjacent to a bone from being cut during an operation onthe bone.

These and other objects of the present invention will be apparent fromthe descriptions and drawings herein. Although every object of theinvention is attainable by at least one embodiment of the invention,there is not necessarily any single embodiment that achieves all of theobjects of the invention.

SUMMARY OF THE INVENTION

An ultrasonic surgical apparatus in accordance with the presentinvention comprises a probe with an operative edge or surface at adistal end, an electromechanical transducer connected to the probe, andan activation circuit connected to the transducer for supplying theretoan electrical waveform having an ultrasonic frequency and an amplitude.The activation circuit includes a signal generator and further includesa power reduction circuit operatively connected to the signal generatorfor inducing the signal generator to automatically reduce the amplitudeof the waveform upon a sensing by the power reduction circuit of reducedload on the probe.

The power reduction circuit may include a load detector, and the loaddetector may include a current sensor. The load detector may furtherinclude a comparator operatively connected to the current sensor forcomparing an output of the sensor with a pre-established referencevalue. The comparator may be a digital device, so that a digitizer isrequired to convert an analog output signal of the current sensor to adigital or binary signal for use by the comparator.

Pursuant to another feature of the present invention, the activationcircuit includes a manually actuatable power switch and the powerreduction circuit further includes a switching circuit operativelyconnected at inputs to the power switch and the comparator and at anoutput to the signal generator. The switching circuit acts toautomatically override an instruction from the manual power switch inthe event that a current reduction indicates that the ultrasonic bladehas penetrated through a bone and encountered soft tissue adjacentthereto.

A surgical method in accordance with the present invention comprisesoperating an ultrasonic cutting tool to cut through bone of a patient,operating a sensor to automatically monitor load on the cutting toolduring the operating of the cutting tool, automatically detecting achange in output of the sensor indicative of a reduced load on thecutting tool owing to a passing of the cutting tool at least partiallythrough the bone, and automatically reducing power to the cutting toolupon the detecting of reduced load on the cutting tool.

The detecting of a change in output of the sensor may include comparingoutput of the sensor with a preselected reference value.

The reducing of power to the cutting tool may include reducing amplitudeof an ultrasonic electrical waveform fed to an electromechanicaltransducer.

The operating of the sensor may include detecting current flow to anelectromechanical transducer connected to the tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is partially a block diagram and partially a schematic sideelevation view, on an enlarged scale, of an ultrasonic bone cuttingapparatus in accordance with the present invention.

FIG. 2 is a block diagram showing details of the apparatus of FIG. 1.

FIG. 3 is a block diagram showing further detailed structure of theapparatus of FIGS. 1 and 2.

DETAILED DESCRIPTION

As depicted in FIG. 1, an ultrasonic surgical apparatus 10 comprises aprobe or tool 12 with an operative (cutting) edge or surface 14 at adistal end. Probe of tool 12 particularly may take the form of anultrasonic bone-cutting blade or drill. Apparatus 10 further comprisesan electromechanical transducer 16 connected to probe 12 for energizingsame with an ultrasonic standing wave of a preselected frequency (orwavelength) determined in part by the dimensions of the probe. Apparatus10 also comprises an activation circuit 18 connected to transducer 16for supplying thereto an electrical waveform having the preselectedultrasonic frequency and a predetermined amplitude. Activation circuit18 includes a signal or waveform generator 20 and further includes apower reduction circuit 22 operatively connected to the signal generatorfor inducing the signal generator to automatically reduce the amplitudeof the electrical waveform upon a sensing by the power reduction circuitof reduced load on probe 12.

Surgical apparatus 10 typically includes further electrical andliquid-supply components as disclosed in U.S. Pat. No. 6,379,371 andU.S. Pat. No. 6,443,969, the disclosures of which are herebyincorporated by reference. For instance, apparatus 10 may incorporate apower switch 24 such as a foot-operated switch.

As illustrated in FIG. 2, power reduction circuit 22 may include a loaddetector 26 and a switching circuit 28. Switching circuit 28 isconnected to power switch 24 and signal generator 20 for enabling theoperation of the signal generator in response to a signal from the powerswitch. Upon receiving a signal from load detector 26 occasioned by adrop in transducer load, switching circuit 28 induces signal generator20 to reduce, or possibly interrupt, the power of the electricalwaveform supplied to transducer 16.

As illustrated in FIG. 3, load detector 26 may include a current sensor30 operatively connected to a lead 32 extending from signal generator 20to transducer 16. Load detector 26 further includes a digitizer oranalog-to-digital converter 34 at an output of the current sensor 30. Acomparator 36 is operatively connected to current sensor 30 viadigitizer 34 for comparing an output of the sensor with apre-established reference value provided by a register 38. Comparator 36is thus a digital device, although an analog device such as anoperational amplifier could alternatively be used.

Comparator 36 compares a digitized output of sensor 30 with thereference value from register 38 and, upon detecting that the currenthas fallen below a pre-established level encoded by the reference value,transmits a signal to switching circuit 28 which in turn causes signalgenerator 20 to reduce the power output to transducer 16, particularlyby reducing the amplitude of the electrical transducer-energizingwaveform. Switching circuit 28 acts to automatically override anoperator-induced instruction from manual power switch 24 in the event ofa current reduction resulting when ultrasonic blade or tool 12 penetratethrough bone and encounters soft tissue adjacent thereto.

A surgical method utilizing the apparatus of FIGS. 1-3 entails usingapparatus 10 to have ultrasonic cutting tool 12 cut through a bone of apatient. Current sensor 30 is operated to automatically monitor load oncutting tool 12 during the operation. A change in output of sensor 30indicative of a reduced load on cutting tool 12 is automaticallydetected owing, the reduction in load arising from a passing of thecutting tool at least partially through the bone.

One automatically reduces power to the cutting tool 12 upon detectingreduced load on the cutting tool. The detecting of a change in output ofsensor 30 may include operating comparator 36 to automatically compareoutput of sensor 30 with the reference value from register 38. Thereducing of power to cutting tool 12 may be implemented by reducingamplitude of an ultrasonic electrical waveform fed to anelectromechanical transducer, i.e., transducer 16.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are proffered by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

What is claimed is:
 1. An ultrasonic surgical apparatus comprising: aprobe including an operative edge or surface at a distal end; anelectromechanical transducer connected to said probe; and an activationcircuit operatively connected to said transducer for supplying theretoan electrical waveform having an ultrasonic frequency and an amplitude,said activation circuit including a signal generator and furtherincluding a power reduction circuit operatively connected to said signalgenerator for inducing said signal generator to automatically reduce theamplitude of said waveform upon a sensing by said power reductioncircuit of reduced load on said probe.
 2. The apparatus defined in claim1 wherein said power reduction circuit includes a load detector.
 3. Theapparatus defined in claim 2 wherein said load detector includes acurrent sensor.
 4. The apparatus defined in claim 3 wherein said loaddetector further includes a comparator operatively connected to saidcurrent sensor for comparing an output of said sensor with apre-established reference value.
 5. The apparatus defined in claim 4wherein said activation circuit includes a manually actuatable powerswitch and wherein said power reduction circuit further includes aswitching circuit operatively connected at inputs to said power switchand said comparator and at an output to said signal generator.
 6. Theapparatus defined in claim 1 wherein said power reduction circuitincludes a current sensor, said sensor being operatively connected to alead extending from said signal generator to said transducer.
 7. Theapparatus defined in claim 1 wherein said load power reduction circuitincludes a comparator configured to compare a sensed load parameter witha pre-established reference value.
 8. The apparatus defined in claim 1wherein said activation circuit includes a manually actuatable powerswitch and wherein said power reduction circuit further includes aswitching circuit operatively connected at an input to said power switchand at an output to said signal generator.
 9. A surgical methodcomprising: operating an ultrasonic cutting tool to cut through bone ofa patient; during the operating of said cutting tool, operating a sensorto automatically monitor load on said cutting tool; during the operatingof said cutting tool, automatically detecting a change in output of saidsensor indicative of a reduced load on said cutting tool owing to apassing of said cutting tool at least partially through the bone; andautomatically reducing power to said cutting tool upon the detecting ofreduced load on said cutting tool.
 10. The method defined in claim 9wherein the detecting of a change in output of said sensor includescomparing output of said sensor with a preselected reference value. 11.The method defined in claim 9 wherein the reducing of power to saidcutting tool includes reducing amplitude of an ultrasonic electricalwaveform fed to an electromechanical transducer.
 12. The method definedin claim 9 wherein the operating of said sensor includes detectingcurrent flow to an electromechanical transducer connected to said tool.